Novel, high performance, phosphorus containing epoxy networks have been prepared and characterized using 1, for example, as the crosslinking moiety, and also using 1 in conjunction with amine terminated polyarylene ethers, such as polysulfone, as the crosslinking reagents. These formulations are useful as flame retardant epoxy networks. They also provide a method of toughening the otherwise brittle cured materials. ##STR1##
The chain extender, 1, can be prepared according to Scheme 1, X =Cl or F. The reaction medium can be a 75:25 vol/vol mixture of dimethylacetamide and toluene (10-12% solids or higher in the reaction medium). Nitrogen atmosphere and 2.05 moles of potassium carbonate can be employed. The phosphorus dihalide monomer and aminophenol can be charged to a reaction vessel equipped with an agitator, nitrogen inlet, and condenser with a Dean Stark trap for water removal. Both dimethylacetamide and toluene are preferably previously dried over calcium hydride, distilled, and maintained under inert atmosphere. The reaction solvents, then the potassium carbonate can be charged, and the temperature is brought up to the reaction temperature. Where X =F, optimum conditions for the reaction ##STR2## are 140.degree. C. for a fourteen hour period. The crude yield of this reaction is nearly quantitative, e.g., about 93%. When X =Cl, the optimum conditions are 160.degree. C. for a period of thirty-six hours and the crude yield is about 60%. Following completion of the reaction, toluene and excess dimethylacetamide can be vacuum stripped from the system until a 30-35% solution of the product in dimethylacetamide is obtained. The product crystallizes in this solution over approximately a six hour period. They are filtered, washed, dried at 60.degree. C. under vacuum, then recrystallized from dimethylacetamide. Finally the recrystallized material is recovered and dried under vacuum at 150.degree. C. to a constant weight.
The instant invention, in its broadest context, involves the use of a "trihydrocarbyl phosphine oxide epoxy curing agent" which is to be understood as encompassing compounds having the preferred structure, for example, of ##STR3## where each of the three groups can be a substituted or unsubstituted phenyl ring (Ar) with the proviso that such compounds also contain epoxy-reactive substituent(s) (shown, for example, by the moieties X). As is well known in the art, such substituents X have active hydrogen and include amine (--NH.sub.2), hydroxy (--OH), carboxy (--COOH), anhydride, and thiol (--SH) moieties. It is preferred that two or more such substituents reside in the compound (e.g., either directly on one or more of the Ar groups or on suitable substituents, e.g., --OAr', on such Ar groups). The above crosslinking agent can be used with other amine terminated polymers, if desired, for example, amine-terminated polyarylene ethers such as the polysulfone oligomers or high polymers. In a broader sense, however, one or more of the Ar groups depicted above can be substituted with another hydrocarbyl group, such as alkyl, especially the Ar group which is not substituted with substituent group "X".